Glass having low-power factor



Patented Jan. 21, 1947 7 GLASS HAVING LOW-POWER FACTOR William H.Armistead, Corning, N. Y., assignor to Corning Glass Works, Corning, N.Y., a corporation of New York No Drawing. Application January 23, 1945,

Serial No. 574,203

6 Claims. (Cl. 106-52) This invention relates to glass compositions andhas for its primary object to provide new and useful glasses havingcertain special characteristics making them suitable as an insulatingmedium for conductors carrying radio frequency currents. As examples ofsuch uses my new glasses are particularly suitable for the insulatinglaminae in electrical condensers and for sealing iron conductors intotubes and envelopes of electronic devices. Mica, which has heretoforebeen used for insulating such condensers, is very expensive and requiresconsiderable selection to insure suitable uniformity in quality. Glass,on the other hand, can be manufactured relatively cheaply and with greatuniformity in composition and properties. However, no glass heretoforehas been devised which combines the desired characteristics to theextent that does the glass to be hereinafter described.

The desired characteristics are:

A power factor less than .06%, as measured at a frequency of onemegacycle at room temperature. The power factor of dielectrics employedin high frequency circuits is very important and with radio frequenciesthe power loss is objectionably large unless the power factor is as lowas .06% or less.

A dielectric constant of at least '7 or 8.

A temperature coefiicient for dielectricconstant less than 200 parts permillion per degree C., is required to meet the Army-Navy specificationsfor fixed, mica-dielectric capacitors having ex--' tremely low powerfactors and adapted for use with relatively large currents. For otherpurposes, the temperature coefficient may be higher. temperaturecoefficient is meant the rate of change of dielectric constant withchange of tern-- perature.

A softening temperature not greater than 625"v in order to permit fusingand sealing the contiguous edges of superposed laminae of the glasswith- 1 but they lack one or more of the above mentioned properties andhence have not been entirely suitable for the purposes in view. Theproblem solved by me has been to obtain all of the desired properties inone glass.

It is commonly believed that alkali metal oxides in' glass are generallydetrimental to the electrical properties of the glass, such as powerfactor, and that they shouldbe omitted or kept to a minimum if low powerfactors and other valuable electrical characteristics are to beobtained. It is also known that glasses having very high silicacontents, in the neighborhood of 100% S102, have exceptionally low powerfactors. Moreover, my prior researches have shown that the unusually lowpower factor of some alkali-free glasses can still further be lowered bythe introduction of alumina. In other words, past experience indicatesthat high silica, low alkali and high alumina contents are conducive tolow power factors,

, However, they also result in high softening tem- ,peratures.

In my pending application Serial No. 558,278, filed October 11, 1944, itis shown that these generalizations do not hold, true.for glassescontaining lead oxide and the alkali metal oxides, but that th presenceof alumina-and a high silica content are detrimental to the power factorof such glasses. Hence it is shown that such glasses possess all of theabove mentioned desirable properties, provided that silica does notexceed 50%, alumina is absent and soda, potash and lithia are present inthe proper ratios.

I have now found that the above properties are also possessed by glasseswhich consist essentially of silica and the oxides of barium, potas:sium, sodium and lithium, the S102 being from 40% to BaO being from 10%to 50%, the total alkali metal oxides (R20) being more than 10% and notless than (lOj-X) where Xis the excess of silica over 50%, the ratioKzO/NazO being from 1.5/1 to 4/1, the ratio being from 4/1 to 19/1, theglass being substantially free from A1203. The lowest power factorsareobtained when the ratio Kzo/Nazo is about 2.3/1 and the ratio(K2O+Na2O)/Li2O is about 9/1. There is no definite upper limit for thetotal contentof alkali metal oxides, but on account of the approach ofinstability and for other practical reasons I prefer to use not-morethan a total of about 25% thereof. With a total alkali metal oxidecontent around 17% to 21% glasses having high expansion coeflicients andlow power factors can be produced'which are particularly suitable forforming glass-to-metal seals with iron. The presence of small amounts ofboric oxide does no harm but has noadvanta-g'e except when it is desiredto lower the expansion coefficient. If desired, the power 1 factor andsoftening temperature can be lowered somewhat further by theintroduction of fluorine, preferably as an alkali fluoride.

As pointed out above, the total alkali content 3 must be not less than(10+X) where X is the excess of silica over 50%. To illustra'tetheCritical effect which alkali metal oxides and also alumina have on thepower factors of my new glasses, the following comparative compositionsin percent by weight and their respective power factors are shown inTable I below. Glass A is a barium-lead glass in which R20 is less than(10+X) and which contains alumina. Except that the lead has beenreplaced by barium, glass B is otherwise the same as glassA. This changeincreased its power factor by an amount equal to 5% of its originalvalue. In glass the S102 and R20 were altered sufficiently to make R20slightly more than (10+X). The result of this was to lower the powerfactor to .063 which is a change of 21% from that of glass B. In glassDthe omission of alumina brought about a further lowering of the powerfactor by another In Table II examples of glasses falling within myinvention and calculatedin percent by weight from their respectivebatches, together with their properties, are given:

I claim:

1. A glass having a power factor 'lessithan 06%, a dielectric constantof at least land a softening temperature less than 625 C., whichconsists essentially of S102, BaO, K20, NazO and Li20, the S102 beingfrom to 65%, BaO being from 10% to the total alkali metal oxides beingmore than 10% and not less than (10+X) where X is the excess of Si02over 50%, the ratio K20/Na2O being from 1.5/1 to 4/1, the ratio.:(K20+Na20)/Li20 being from 4/1 to 19/1, the 'glass being substantiallyfree from M203.

2. A glass having a power factor less than 06%, a, dielectric constantof at least 7 and a softening temperature less than 625 0., whichconsists essentially of Si02, 'BaO, K20, Na20 and L120, the Si02 beingfrom 40% to BaO being from 10% to 50%, the total alkali metal oxidesbeing more than 10% and not less than (IO-,I-X) where X is the excess ofSi02 over 50%, the-ratio K20/Na2O being about 2.3/1; the ratio .(KzO-i-Na20) /Li20 being about 9/1, the glass beingsubstantially free fromA1203.

3. A glass having a power factor :less than .06%, a dielectric constantof at least 7 and ;a

- softening temperature less than 625 C., which consists essentially ofS102, Ba0, K20, N220, and Li2O,'the Si02 beingfrom 40% to 65%, BaO beingfrom 10% to 50%, the total alkali metal oxides being more than 10% andnot less than (10+X) where Xis the excess of S102 over 50%,, the ratioK2O/Na20 being from 1.5/1 to 4/1, the ratio (Kz0+Na20)/Li20 being from4/1 to 19/1, the glass being substantially .free from A1203, and 'con-35 taining fluorine.

4. A glass having a power factor less than 06% and an expansioncoefficient about 128x10- Table II S102 50 50 60. 0 40. 0 50. 0 47. 047. 0 47. 0 BaO... '35 34 20. 0 40. 0 25.0 35. 0 35.0 350 K10 10 10 12.612.6 15. 7 12.10 11. 3 10.1 NnO 4 4 5.4 15.4 6.8 5.1 4.9v 4.3 L 1 1 2. 02. 0 2. 5 9 1:8 3. 6 NazSiFu l.- 1 Power factor, per cent 052 050 058041 045 045 043 046 Dielectric constant 8. 0 8.0 7. 7 8. 4 8. 4 8.1 '8.1 '8. 1 Temperature coeflicient, 132 132 Softening temp, .O 618 607 590543 534 588 577 557 Expansion coeff. X10 1 117 117 119 137 136 128 .128128 About 1% of Sb20s was introduced into the batches for the purpose offining the glasses. This has no substantial :effect on their properties.The values for power factor were measured at 'a frequency of onemegacycle by the method known as A. S. T. M. D--42T,'set forth on page1148 et seq., part III of the A. S. T. M. Standards for 1942.

It will be noted that the power factors of the above glasses aresubstantially below 06% and that their other properties are alsosuitable for the purposes set forth above. Glass 2 illustrates theeffect of adding fluorine to glass 11 and the power factor and thesoftening point were there- I by lowered. Glasses 1 and .2 areparticularly suit- I able 'for'insulating laminaein lieu of mica inlarge-current, fixed condensers or capacitors. Glasses '6, 7, and8,which have expansioncoefiicientsnear that of iron, are particularlyuseful .as iron-sealing glasses in the manufacture of glass-to-metal:seals.

cm. per cm. per degree 0., which consists essentially of S102, BaO, K20,N200, and L120, the

S102 being from 40% to 65%, BaO from 10% to 50%, total alkali metaloxides from about 17% to about 21%, the ratio K20/Na20 being from 15/1to 4/1, the ratio (K2O+Na20')/Li20 being from 4/1 to 19/1, the glassbeing substantially free from A1202.

5. 'A' glass having apower factor less than 06%, a dielectric constantof at least 7 and a softening temperature less than 625 C., which hasthe approximate composition 47% S102, 35% BaO, 10% to 12% K20, 4% to5.5% iNazO, and ;9% to 3.6% Li2O. V

)WILLIAMH. ARMI-STEAD.

6..A .g'lass having a power factor :less .than .06%, a dielectricconstant 'of at least 7 and a

